The present invention relates to a displacement control valve for variable displacement compressors, more specifically, to a control valve that controls the amount of gas flow to and from a crank chamber to vary the compressor displacement.
In a typical variable displacement compressor, the inclination of the swash plate varies in accordance with the pressure in a crank chamber (crank pressure Pc). To control the crank pressure Pc, either the flow rate of refrigerant gas delivered to the crank chamber or the flow rate of refrigerant gas released from the crank chamber must be controlled.
The crank chamber is connected to a discharge chamber by a supply passage and to a suction chamber by a bleeding passage. To control the flow rate of gas delivered to the crank chamber, an inlet control valve is located in the supply passage. The inlet control valve adjusts the flow rate of refrigerant gas supplied to the crank chamber from the discharge chamber, thereby setting the crank pressure Pc to a desired level.
To control the flow rate of gas released from the crank chamber, an outlet control valve is located in the bleeding passage. When a piston compresses refrigerant gas in an associated cylinder bore, refrigerant gas in the cylinder bore leaks into the crank chamber between the surface of the piston and the wall of the cylinder bore. The leaking gas is referred to as blowby gas. The blowby gas increases the pressure of the crank chamber. The outlet control valve adjusts the flow rate of refrigerant gas flowing from the crank chamber to the suction chamber to set the crank pressure Pc to a desired level.
One advantage of an inlet control valve is that the crank pressure Pc can be increased quickly. However, to maintain the crank pressure Pc, the flow rate of refrigerant gas flowing into the crank chamber must be the same as that flowing out of the crank chamber. In other words, a relatively great amount of gas is required to maintain the crank pressure Pc.
An outlet control valve, on the other hand, has a relatively simple structure and automatically controls the valve opening size. One advantage of an outlet control valve is that only a small supply of gas is required to maintain the pressure in the crank chamber. However, an outlet control valve takes a relatively long time to raise crank pressure Pc. Therefore, a compound control valve, which has advantages of inlet and outlet control valves, has been introduced.
Japanese Unexamined Patent Publication No. 5-99136 discloses a compound control valve having an inlet valve portion, an electromagnetic actuator, an outlet valve portion and a transmission rod. The inlet valve portion includes an inlet valve body and a spring. The inlet valve body is moved by the rod to open and close a supply passage. The spring urges the inlet valve body downward, or in a direction closing the supply passage. The electromagnetic actuator urges the rod upward against the force of the spring. The outlet valve portion is located between the inlet valve portion and the actuator and is coupled to the actuator.
The outlet valve portion includes a diaphragm and an annular outlet valve body. The outlet valve body adjusts the opening size of a bleeding passage, which connects the crank chamber to a suction chamber, based on the suction pressure Ps of the compressor. The outlet valve body is engaged with a step formed on the transmission rod. When the rod is moved downward, the outlet valve body is moved integrally with the rod. When the rod is moved upward, the outlet valve body contacts a valve seat formed in the valve housing to close the bleeding passage. If the rod is moved further upward, the rod does not move the outlet valve body while moving the inlet valve body upward. In other words, the rod functions as a guide to support the outlet valve body.
The control valve sets a target suction pressure based on the level of a current supplied to the actuator. When the crank pressure Pc needs to be quickly increased, a current, the level of which is greater than a predetermined level, is supplied to the actuator. Accordingly, the actuator moves the rod upward to cause the outlet valve body to close the bleeding passage. The actuator further moves the rod upward to quickly move the inlet valve body upward to open the inlet valve portion. In other words, the control valve functions as an outlet control valve when the compressor is operating in a normal state and functions as an inlet control valve when the crank pressure Pc needs to be raised quickly. Therefore, during normal operation, the control valve requires only a small flow rate of refrigerant gas to maintain the crank pressure Pc, and when necessary, the crank pressure Pc can be changed quickly.
The variable displacement compressor of the above publication has an auxiliary supply passage, which connects the discharge chamber with the crank chamber. The auxiliary supply passage supplies refrigerant gas to the crank chamber from the discharge chamber when the amount of blowby gas to the crank chamber is insufficient. Even if the inlet valve body contacts the valve seat to completely close the main supply passage, the crank chamber is connected to the discharge chamber by the auxiliary supply passage. Although the main supply passage and the auxiliary supply passage have the same function of supplying refrigerant gas from the discharge chamber to the crank chamber, the supply passages are independent. This complicates the machining of the housing and increases the costs.
Also, a rod that serves as a sliding guide for supporting the inlet valve body complicates the structure of the control valve and is not suitable for mass production.
Since the rod and the outlet valve body are movable parts, the contacting portions of the surface of the rod and the outlet valve body preferably slide smoothly relative to each other. Also, when the outlet valve body contacts the corresponding valve seat, the rod and the outlet valve body preferably form an effective seal. However, the rod and the outlet valve body violently slide relative to each other. Therefore, even if the machining accuracy and slide resistance are improved, the sealing effectiveness between the outlet valve body and the rod will not be sufficient. An inadequate seal effectiveness causes gas to leak from the crank chamber to the suction chamber. Hence, the crank pressure Pc cannot be accurately controlled.
The axial length of the outlet valve body may be increased such that the outlet valve body is cylindrical. This will improve the sealing effectiveness between the outlet valve body and the rod but will increase the weight of the outlet valve body. Increasing the weight of the outlet valve body deteriorates the performance of the outlet valve.
Accordingly, it is an objective of the present invention to provide a displacement control valve that has a simple structure and accurately controls the pressure in a crank chamber.
To achieve the above objective, the present invention provides a control valve for controlling the displacement of a variable displacement type compressor. The compressor includes a crank chamber, a suction pressure zone, the inner pressure of which is suction pressure, a discharge pressure zone, the inner pressure of which is discharge pressure, a bleed passage for bleeding gas from the crank chamber to the suction pressure zone, and a supply passage for supplying gas from the discharge pressure zone to the crank chamber. The control valve comprises a valve housing. An outlet valve portion is located on the bleed passage to control the opening of the bleed passage. An inlet valve portion is located on the supply passage to control the opening of the supply passage. A shaft-like transmission mechanism extends between the outlet valve portion and the inlet valve portion to connect the outlet valve portion to the inlet valve portion. The transmission mechanism moves axially. A through hole is located in the inlet valve portion to receive a part of the transmission mechanism. The through hole constitutes a part of the supply passage. A clearance is formed between the transmission mechanism and a surface that defines the through hole to constantly connect the discharge pressure zone to the crank chamber.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.